Effects Of Zucchini Cucurbita Zucchini L. On The Host-Specialization Of Cotton-Melon Aphid,Aphis Gossypii Glover

The cotton aphid, Aphis gossypii Glover, is one of the main pests and it causes serious damage for cotton, melon and various horticultural plants. The aphid species has formed high specialization to various host plants because of the long-term living on congener or similar plants. However, we have not known whether the differenthost specialized biotypes could convert exchange, how host plants influence the host specialization, and whether the body form of A. gossypii Glover and host selection would change as the change of the host specialization. The cotton-and cucurbits-specialized aphids were used in this study to research the effects of zucchini Cucurbita zucchini L. on host use, selection and morphological traits, and the following results were attained:The results of host transplantation showed that the cotton-and cucurbits-specialized aphids could not exchange their host plants directly. However, both of them could use zucchini Cucurbita zucchini L. very well, and could establish population on zucchini. After feeding on the zucchini for five consecutive generations, the cotton-specialized aphids obtained the ability to use cucumber and could establish on it. However, after feeding on zucchini for seven generations, the cotton-specialized aphids would lose the ability to use the original host plant, cotton, and converted into the cucurbits-specialized biotype. The cucurbits-specialized aphids had the stronger ability to use zucchini. The experience feeding on zucchini had no influence on the preference of cucurbits-specialized aphids on cucumber, and they still could not use cotton as they were reared17generations on zucchini.The result of host selection experiments showed that both the cotton-and cucurbits-specialized aphids had their preference for cotton and cucumber, respectively. The selecting rate of cotton-specialized aphids after feeding on zucchini for several generations to cotton leaves gradually decreased, and it was37.14%at the third generation but it was only2.86%at seventeenth generation reared on zucchini. On contrary, the selecting rate to cucumber increased gradually, the value was28.10%at third generation and became41.43%at seventeenth generation on zucchini. The cucumber biotype aphids preferred zucchini leaves at any time.The numerical traits of the form of aphids showed that significant difference existed between the cotton-and cucurbits-specialized aphids. The body sizes of cucurbits-specialized aphids were larger than the cotton-specialized aphids. As the generations of the cotton-specialized aphids cultivated on zucchini increased, all the sizes of form traits magnified and became as similar as the cucurbits-specialized aphids. Particularly, the femur and tibia of the fore-and middle-legs greatly prolonged and reached up to the level of the cucurbits-specialized aphids. This kind of growth of legs in the cotton-specialized aphids feeding on zucchini was very suitable to adapt the situation of cucurbits plants with long hairs. The values of morphological characteristics of the cucurbits-specialized aphids feeding on zucchini changed little.In summary, the change in morphological characteristics and host select capacity of the cotton-specialized aphids on the zucchini made the breaking of the host-specialization, and the cotton-specialization converted into the cucurbits-specialization. And the given host plant played an important role on the formation and maintenance of the host specialization in aphids.